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Advantest R3273 / R3267 Repair

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chick0n:
I checked on the low signal problem again.

Everything is back to stock...Voltage Regulator is in...

I applied -10dbm CAL Signal to analyzer input, set analyzer to zero span... shows as -50dbm on analyzer.

I disconnected the connection between 1st mixer output and 2nd mixer input. Then I connected Power Sensor to 1st mixer output. Shows about -13dbm at 4,3GHz....

Then I set microwave source to 4,3GHz -13dbm, and injected to 2nd mixer input. Analyzer Shows -13dbm correctly.  :wtf:

Then I reconnected 1st mixer to 2nd mixer. Analyzer shows -50dbm again...  :-//

I dont know whats right or wrong in this world anymore...

Gyorgy Albert:
Your power meter is a broadband device, I mean it is not a selective receiver. You can measure the -13 dBm level, but it does not mean that the carrier frequency which cames out from the 1st IF  it is there where it should be (a relatively small frequency deviation could be enough, to measure a low level. Of course all these will also depend on the selected RBW). Try to feed from the external generator (which preferably is connected to the same reference clock as the analyzer) a 30 MHz -10dBm signal to the input of the analyzer. If this works, and you will measure a correct level, it means that your 30 MHz CAL signal is out of sync, and it is not at 30 MHz (which would be a bit strange). If this doesn't work either, than you might have a shift in the frequency of the first local oscillator. Which is possible, even if it seems locked. The phase lock of the YIG is a multi loop PLL, with several conversions, and if you change some settings in the maintenance mode, you can easily detune it (and will be locked to a shifted frequency. But if you have not changed the settings in the maintenance mode, this should not be the case). So you have to find out 2 things: if your CAL signal is sharply 30 MHz, and if your 1st LO is spot on the right frequency. They both are locked to the 10 MHz reference frequency.

Also please note: The 4.1 GHz IF is used only for the low frequency band (if I am right below 3.5 GHz). For higher frequencies it is skipped, and the IF is directly 421 MHz. Eventually, check the RF path measured level, with some RF signal in the higher bands (above 4 GHz). Just to be sure, that this path which does not use the 4.1GHz IF is working or not.

chick0n:
Youre right, with Power Meter I measure all "Peaks" in the Spectrum at the same time... Also I "misused" the Scalar Detector of my Marconi 6203 as Power Sensor, because it is more Sensitive.

I checked the cal signal with a good analyzer. Its OK.

My freq. Counter and Microwave source are synched to the R3273 Ref.

I connected the 1st mixer IF out to the counter, it measures exactly 4.23154GHz. So the strongest Peak on the 1st mixer output seems about correct. (Service Manual says 1st IF is 4.2314GHz)

Also, the "torque" of the screws on the 1st mixer lid make a difference in output power. All screws tight = -23dbm. Loosing some screws = -13dbm. Lid open = -27dbm. ;)

chick0n:
Ok...I measured again with the 4.5Ghz Low Pass Filter in place at the IF Out.

I think, what happens is, sometimes the counter catches the YTO-LO frequency at the IF Out (~4.26142GHz), and sometimes it catches the IF frequency (4,23154GHz).

The Power Sensor measures both, and maybe more Mixer Products...

The IF gets filtered better at a later stage, with a Bandpass Filter.

chick0n:
Today I found out, SHIFT + TRANSIENT + 882323 + Hz, does indeed Trigger a hidden menu.

Its the Maintenance mode of the DSP-Card. You can acces under CONFIG - Comm Sys. - Maintenance.

Smacks on forehead...  :palm:

So we finally got that sorted out...and we know definately, the Debug Menu gets triggered somewhere else...

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